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Is my boiler pressure too high?


Whenever you’re looking to install a new boiler or simply have maintenance done on your current model, it’s vitally important to know how a boiler loses pressure, and how to repressurise a boiler should you be faced with this issue. Having this key skillset will help to make your heating system more energy efficient and keep costs down.

A boiler moderates your central heating and your water, though it is important to remember that boiler pressure and water pressure are two separate things. Boiler pressure refers to the pressure of hot water running in your sealed central heating system, while water pressure is the pressure of the water coming through your taps.

Boiler pressure is important for several reasons. Primarily, if you have low boiler pressure your system could cut out, preventing your central heating from working. Alternatively, if there is high boiler pressure, the system will be strained beyond normal capacity and could potentially fail.

What is the correct pressure for a boiler?

While not every boiler has the same pressure requirements, most central heating systems perform within the range of 1 to 2 bar, which is between 14 and 29 pounds per square inch (psi). The exact pressure of your combination and system boiler can be measured on the boiler pressure gauge, which is generally visible on the front of the control panel.

How to top up the pressure on boilers

The most commonly used method when it comes to boiler pressure top up is to check and use the filling link/loop. These come in three different varieties depending on your unit’s age and manufacturer:

  • External filling link – as the name suggests, this filling loop is located outside of the unit, usually underneath or to the side of the system.
  • Keyed filling link – this is generally located internally, beneath the system and requires a specialised key to operate, which is provided with the boiler.
  • Keyless filling link – this is operated by an integral lever beneath the boiler.

Once located, you need to twist your respective valve and keep an eye on the pressure gauge. You’ll hear the sound of flowing water as the system adjusts itself and the pressure gauge will start to rise. When the gauge reaches 1.1-1.2, it’s at the correct boiler pressure and your boiler has been topped up sufficiently. This process should only need to be done once or twice a year and any increase on this might be an indication of a leak in the water system.

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What happens if my boiler pressure is too high?

Just as important as knowing how to increase boiler pressure is knowing how to reduce it, should your boiler pressure gauge start to exceed 3.0. As previously mentioned, if your boiler is consistently running at a higher pressure it could cause a system failure or damage to your home. A good indicator as to whether your boiler pressure is too high is if you can see water leaking or dripping from the pressure relief valve, usually located on outside wall where the unit has been installed. In some cases, a leaking pressure relief valve can cause corrosion to build on your boiler's pipework. You may need a new boiler if these problems continue.

How to reduce boiler pressure

An effective way to reduce pressure is to drain water from the system. This can be achieved by locating a drain point, which is usually underneath a radiator, and opening it with a spanner, pliers, or an Isle of Man key. As water is drained, keep an eye on boiler pressure gauge to ensure it stays within the effective parameters. While adjusting your radiators, it may also help to bleed them.

How to bleed a radiator

Bleeding radiators is a quick and easy process, and most people can perform this task themselves. The only tool that is necessary is a radiator key, which can be bought cheaply from any DIY shop. From here, you only need to find and operate the release valve, which is usually located on the top and side of a radiator unit. As the valve is turned, air bubbles in the radiator are released, as is excess water. For this reason, it’s important to have a dry cloth nearby as well as a container to catch the water in. In the process, the boiler loses pressure, bringing it back to a normal level that increases energy efficiency in your home. As with using the drainage valve, it is vitally important that this process is performed when the boiler is cold.

Take a look at our guide to bleeding radiators here.

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